Continued efforts will be made to investigate the various forms of naturally occuring chronic neurological diseases in dogs caused by canine distemper virus (CDV). Attempts to isolate and detect infectious and defective CDV from dogs diagnosed as old dog encephalitis and chronic distemper encephalitis will be continued. CDV isolates from dogs with chronic neurological diseases will be compared with laboratory strains of CDV. Comparisons will be made by animal susceptibility, cell culture properties and immunological reactivity. Viral polypeptides will be compared by immunoprecipitation techniques. Sera from dogs with various forms of encephalitis caused by CDV will be analyzed for antibodies to structural viral polypeptides using recent isolates as well as laboratory strains of CDV. Studies to identify CDV-specific polypeptides directly in tissues will be attempted in order to determine the physical state of th CDV in persistently infected tissues of dogs. Attempts to assess the identities and amounts of viral polypeptides at any moment from the time of tissue excision to various subsequent times of tissue explant, before and after production of CDV, will be made. These studies on the canine distemper model are aimed to provide a better understanding of the mechanism of viral persistence in the central nervous system and of the pathogenesis of virus-induced demyelinating encephalitis.